Just to clear up some confiusion between the Username and Name setting in the profile that @ThistleAli brought up…
Your username is what you use to sign in and what is your public name. It will appear next to your posts and people can mention you in posts (like I just did there) with it.
When looking at your profile, they can also see your regular name. This can have spaces and other characters that your username can’t have. They can be the same - you can leave your name blank if you like.
It’s up to you. But that’s what they do.